Documentation: NavigationViewModel

1. Purpose

NavigationViewModel is a Prism-based ViewModel responsible for managing the navigation region within the DTS Viewer application's shell. It serves as a mediator between the INavigationView and the application's navigation infrastructure, handling notification popups via InteractionRequest and providing a bindable ContextNavigationRegion property for dynamic content injection. The class inherits from BaseViewModel<INavigationViewModel> and implements INavigationViewModel.

2. Public Interface

Constructor

public NavigationViewModel(
    INavigationView view, 
    IRegionManager regionManager, 
    IEventAggregator eventAggregator, 
    IUnityContainer unityContainer)

Initializes the ViewModel, sets the view's DataContext to itself, creates NotificationRequest and ConfirmationRequest instances, and subscribes to the RaiseNotification event via the EventAggregator.

Properties

Property	Type	Access	Description
`NavigationView`	`INavigationView`	`get`	Stores the associated view instance.
`NotificationRequest`	`InteractionRequest<Notification>`	`get`	Used to raise notification dialogs.
`ConfirmationRequest`	`InteractionRequest<Confirmation>`	`get`	Used to raise confirmation dialogs.
`ContextNavigationRegion`	`object`	`get/set`	Gets or sets the content of the `NavigationRegion` on the view. Raises `OnPropertyChanged` on set.
`HeaderInfo`	`string`	`get`	Returns the constant string `"NavigationRegion"`.
`IsBusy`	`bool`	`get/set`	Throws `NotImplementedException`.
`IsDirty`	`bool`	`get`	Throws `NotImplementedException`.

Methods

Method	Return Type	Description
`Initialize()`	`void`	Override. Empty implementation.
`Initialize(object parameter)`	`void`	Override. Casts `parameter` to `IShellViewModel` and assigns to `Parent` field.
`Activated()`	`void`	Override. Throws `NotImplementedException`.
`Cleanup()`	`void`	Override. Throws `NotImplementedException`.
`CleanupAsync()`	`Task`	Throws `NotImplementedException`.
`InitializeAsync()`	`Task`	Override. Throws `NotImplementedException`.
`InitializeAsync(object parameter)`	`Task`	Override. Throws `NotImplementedException`.

Events

Event	Type	Description
`PropertyChanged`	`PropertyChangedEventHandler`	Declared with `new` keyword, hiding the base implementation. Raised via `OnPropertyChanged`.

3. Invariants

NavigationView is set once in the constructor and never reassigned.
ContextNavigationRegion always accesses ((NavigationView)NavigationView).NavigationRegion.Content, requiring the concrete NavigationView type.
HeaderInfo always returns the literal string "NavigationRegion".
The RaiseNotification event subscription is established at construction time and never unsubscribed.
Parent is only set via Initialize(object parameter) and expects an IShellViewModel instance.

4. Dependencies

This module depends on:

DTS.Common.Base — BaseViewModel<T>
DTS.Common.Events — RaiseNotification event, NotificationContentEventArgs, NotificationContentEventArgsWithoutTitle (implied by usage)
DTS.Common.Interface — INavigationViewModel, INavigationView, IShellViewModel
Microsoft.Practices.Prism.Events — IEventAggregator
Microsoft.Practices.Prism.Interactivity.InteractionRequest — InteractionRequest<T>, Notification, Confirmation
Microsoft.Practices.Prism.Regions — IRegionManager
Microsoft.Practices.Unity — IUnityContainer

What depends on this module:

Unclear from source alone — The IShellViewModel interface suggests a parent shell consumes this ViewModel, but the exact consumers are not visible in this file.

5. Gotchas

Many members throw NotImplementedException: IsBusy, IsDirty, Activated(), Cleanup(), CleanupAsync(), InitializeAsync(), and InitializeAsync(object parameter) are all stubs that will crash if invoked. This indicates incomplete implementation.
Broken abstraction in ContextNavigationRegion: The property casts INavigationView to the concrete NavigationView type to access NavigationRegion.Content. This violates the interface contract and creates tight coupling.
Incorrect XML documentation: The constructor's XML comment states it "Creates a new instance of the TechnologyDoFrontEditViewModel" — this is a copy-paste error and does not match the actual class name.
Event hiding: The PropertyChanged event and OnPropertyChanged method are declared with new, hiding the base class implementation. This could lead to unexpected behavior if consumers expect the base event to fire.
No event unsubscription: The RaiseNotification event subscription in the constructor has no corresponding unsubscription in Cleanup() (which throws anyway), potentially causing memory leaks.
Commented-out dead code: A GetRegions() method is entirely commented out, suggesting unfinished or abandoned functionality.

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